1. Field of the Invention
This invention relates to photochemical reactions involving gelatin and other substrates and, more particularly, to photochemical reactions by which a surface of a gelatin or other body can be attached to a second surface of the same or another body. The two surfaces can be the same or different and can be gelatin, nylon, glass, or any other material, synthetic or natural, having a molecular structure which includes either a nitrogen functionality or hydroxyl groups.
2. Description of the Prior Art
Photoinitiated polymerization reactions have found commercial use in printing inks and in various coating compositions. Examples of such coating compositions include those used in filling the surfaces of particle board, those used in coloring or staining wood surfaces, those used to apply a final clear glass coating, those used to produce flexible coatings on vinyl floor surfaces, and those used in applying both base coats and clear vinyl coatings on metal surfaces, particularly metal surfaces of automobiles and components thereof.
Photoinitiated polymerizations as used in the foregoing applications involve a polymerizable monomer or a polymerizable composition and a photoinitiator, in addition to various additives which may be required for the particular application. The most common polymerizable monomers and compositions are acrylics, polyesters, and blends of styrene with maleic anhydride. Benzoin ethers, and related acetals, "Hammond's initiators", and various acetophenone derivatives are presently the most generally used photoinitiators. Polybrominated diphenyls have also been used, and cationic photoinitiators have found some commercial use as have benzoyl peroxide and many of its derivatives.
Examples of acrylic monomers and oligomers that have been used in photopolymerizable printing inks include pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexacrylate, ditrimethylolpropane tetraacrylate, epoxy acrylates, epoxidized drying oil acrylate, bisphenol A diglycidyl ether acrylate, modified bisphenol A epoxy acrylate, aliphatic epoxy acrylates, polyacrylate carbamates, reaction products of a hydroxyl containing acrylate, a diisocyanate and a hydroxyl containing moeity (resin, alkyd, drying oil, polyester, etc.), polyester acrylates, polyether acrylates, acrylated alkyds, melamine acrylates, monoacrylates, hydroxybutyl acrylate, dicyclopentadiene acrylate, 1, 6-hexanediol monoacrylate, cyclohexylacrylate, triacrylates, trimethylol propane triacrylate and pentaerythritol triacrylate.
Benzoin ethers and related acetals which are used as photoinitiators usually have the general formulae: ##STR1## where R is an alkyl group having from one to eighteen carbon atoms.
Hammond's initiators have the general formula: ##STR2## Benzophenone is a specific example of one of the Hammond's initiators that has been used. Many acetophenone derivatives have been used as photoinitiators; two specific ones have the formulae: ##STR3##
Generally, photosensitive peroxides and peresters contain an absorbing chromophore and a homolytically labile 0--0 bond. An example is p-benzoyl t-butyl perbenzoate: ##STR4##
Two photopolymerizable printing ink compositions which have been disclosed in the published literature are set forth below:
______________________________________ Weight Percent ______________________________________ Colored Pigment 25.0 Polyol Acrylate 25.0 Epoxy Acrylate 40.0 Mixed Photoinitiators 6.5 Inhibitor 0.1 Trimethylolpropane 3.4 Triacrylate Colored Pigment 20.0 Polyol Acrylate 15.0 Epoxidized Soybean 30.0 Oil Acrylate Epoxy Acrylate 20.0 Mixed Photoinitiators 12.0 Inhibitor 0.1 Trimethylolpropane 2.9 Triacrylate ______________________________________
In general, photopolymerizable printing inks, coatings, and the like are applied to substrates and exposed to light of a suitable wavelength to initiate cure, which then proceeds at an extremely rapid rate.
Cationic photoinitiators, for example the diaryliodonium and triarylsulfonium salts which are subsequently identified herein, and acrylic and other monomers such as ethers and epoxides produce polymers when the cationic photoinitiators are photolyzed in the presence of anions such as PF.sub.6.sup.31 , AsF.sub.6.sup.-, and SbF.sub.6.sup.- and an appropriate monomer. The anions generate the corresponding Lewis acids, PF.sub.5, AsF.sub.5, and SbF.sub.5, or H+, which induce polymerization. Similarly, diaryliodonium salts, when subjected to photolysis, produce cation radicals which, in the presence of a solvent, produce aryl iodides, aryl radicals, and protonic acid, the last being a cationic catalyst for polymerization. Examples of typical operable diaryliodonium salts have the following formulae: ##STR5##
Triarylsulfonium salts, when photolyzed, undergo reactions directly analogous to those of diaryliodonium salts, also producing protonic acid. Examples of typical operable triarylsulfonium salts have the following formulae: ##STR6##
Cationic polymerization catalysts are effective with various vinyl monomers, including the acrylics discussed above and styrene, with cyclic ethers, cyclic formals and acetals, with sulphur containing monomers, with organosilicon monomers and with various materials having an epoxy function, including monofunctional epoxys, difunctional epoxys, and epoxy prepolymers and higher oligomers.
Thin polymer films, called photoresists, formed photochemically upon solid surfaces are also known. One of the first organic photoresists was a poly (vinyl cinnamate) system, produced by reacting cinnamoyl chloride and poly (vinyl alcohol) to produce photoreactive cinnamate esters. The cinnamate esters can be applied to a substrate and exposed to 300 nanometer light in a desired pattern; the exposure insolubilizes the exposed portions of the film to form a resist in the pattern in which the film was exposed to light. The unexposed portions of the film can then be washed away to expose the substrate for chemical treatment. Photoresists on silicon chips carrying a silicon dioxide coating are widely used in producing silicon integrated circuits.
3. The Instant Invention
The present invention is based upon the discoveries: (1) that the two mating parts which form a gelatin capsule can be bonded to one another by applying to their mating surfaces a thin coating of a solution of p-benzoyl tert-butyl perbenzoate in methyl methacrylate, assembling the two parts into a capsule, and irradiating the methyl methacrylate solution through the outer gelatin layer with the output of a medium/high pressure mercury resonance lamp; (2) that a gelatin capsule can be bonded to a nylon, glass or paper substrate by coating the substrate with a blend of p-benzoyl t-butyl perbenzoate and a commercially available printing ink (hereinafter identified as "Printing Ink A"), placing the capsule on the coating on the substrate and irradiating the coating through the capsule with the output of a medium/high pressure mercury resonance lamp; and (3) that two flat sheets of glass can be bonded to one another by confining, between two of the major surfaces thereof, a solution of p-benzoyl tert-butyl perbenzoate in methyl methacrylate and diethylene glycol bis (allylcarbonate) and irradiating the methyl methacrylate/diethylene glycol bis (allyl carbonate) solution with the output of a UV sun lamp. In view of these discoveries, it was appreciated that a method for locking two surfaces to one another had been invented, where both surfaces were of a material which has hydroxyl or amino groups in its structure, and that the method involved three embodiments comprising:
in a first instance, the steps of bringing the two surfaces together with a cross-linking monomer such as methyl methacrylate and a photoinitiator therebetween and irradiating the interface between the two surfaces with radiation at a wave length to which the photoinitiator is sensitive, but to which at least one of the materials is substantially transparent, and controlling the time of irradiation and the intensity of the radiation so that the two surfaces are locked relative to one another;
in a second embodiment, using a surface to which a monomer which is capable of photochemically initiated addition or condensation polymerization, e.g., an ethylenically unsaturated monomer, has been grafted and the steps of bringing the two surfaces together with a photoinitiator therebetween and irradiating the interface between the two surfaces with radiation at a wavelength to which the photoinitiator is sensitive, but to which at least one of the materials is substantially transparent, and controlling the time of irradiation and the intensity of the radiation so that the two surfaces are locked relative to one another; and
in a third instance, the steps of reacting the material at the first surface to produce a photoresist, reacting the material at the second surface to produce a photoresist, bringing the first and second photoresist surfaces together and irradiating the interface between the two surfaces with radiation at a wavelength to which both of the photoresists are sensitive, but to which at least one of the materials is substantially transparent, and controlling the time of irradiation and the intensity of the radiation so that the two surfaces are locked relative to one another.